Four-Dimensional Stimuli-Responsive Hydrogels Micro-Structured via Femtosecond Laser Additive Manufacturing

Abstract

Rapid fabricating and harnessing stimuli-responsive behaviors of microscale bio-compatible hydrogels are of great interest to the emerging micro-mechanics, drug delivery, artificial scaffolds, nano-robotics, and lab chips. Herein, we demonstrate a novel femtosecond laser additive manufacturing process with smart materials for soft interactive hydrogel micro-machines. Bio-compatible hyaluronic acid methacryloyl was polymerized with hydrophilic diacrylate into an absorbent hydrogel matrix under a tight topological control through a 532 nm green femtosecond laser beam. The proposed hetero-scanning strategy modifies the hierarchical polymeric degrees inside the hydrogel matrix, leading to a controllable surface tension mismatch. Strikingly, these programmable stimuli-responsive matrices mechanized hydrogels into robotic applications at the micro/nanoscale (<300 × 300 × 100 μm3). Reverse high-freedom shape mutations of diversified microstructures were created from simple initial shapes and identified without evident fatigue. We further confirmed the biocompatibility, cell adhesion, and tunable mechanics of the as-prepared hydrogels. Benefiting from the high-efficiency two-photon polymerization (TPP), nanometer feature size (<200 nm), and flexible digitalized modeling technique, many more micro/nanoscale hydrogel robots or machines have become obtainable in respect of future interdisciplinary applications.

3D printed microfluidics: advances in strategies, integration, and applications

“…Recently, positive photoresists such as AZ 4562 (MicroChemicals), were used to print monolithic microfluidic structures that could be integrated with porous membranes and potentially other functional components such as pumps and filters. 73 Beyond rigid structures printed with photoresists, two-photon curable silicone 69 and hydrogels such as polyethylene glycol diacrylate (PEGDA), 68,70,74 represent ideal candidates for printing biocompatible and mechanically compliant microfluidic structures. Indeed, recent progress has demonstrated the printing of unique stimuli-responsive hydrogel microstructures with low-power lasers (as low as 0.1 Joule per laser pulse) in the visible spectrum.…”

Editorial for the Special Issue on Laser Additive Manufacturing: Design, Processes, Materials and Applications

“…This Special Issue article focuses on continuous-wave (CW) laser additive manufacturing (e.g., laser powder bed fusion (L-PBF), laser direct energy deposition (L-DED)), but also includes pulsed-wave (PW) laser advanced manufacturing (e.g., femtosecond-pulsed laser machining, two-photon polymerization [5]) and heat treatment annealing processes [6]. It is worth mentioning that laser additive composite manufacturing (e.g., CW L-PBF & CW L-DED [7]), laser subtractive composite manufacturing (CW laser and PW femtosecond laser machining [8]) and laser additive & subtractive composite manufacturing (CW L-PBF and PW femtosecond laser surface ablation modification [9]) are also current research frontiers in laser advanced manufacturing.…”

“…This Special Issue article covers a wide range of forming materials, including steel [1,9] and other iron-based alloys [11], magnesium alloys [3], titanium alloys [6,12], copper alloys [7], aluminum alloys [13], composites (e.g., CF/PA12 [4], copper/titanium-coated diamond [14]) and, in particular, metallic multi-materials (e.g., NiTi/CuSn10 [2], copper/steel [7]) and 4D-printing materials (e.g., NiTi shape memory alloys [2,15], smart materials for soft interactive hydrogel [5]). et al [12] investigated types of Ti-6Al-4V (TC4) materials with different porosities fabricated via L-PBF using different printing parameters.…”

“…The findings of this Special Issue article are expected to provide guidance and reference for scientists and engineers in the fields of aerospace (e.g., copper/steel multi-material engine thrust chambers [7], titanium alloy lightweight structural components [6,12]), biology (e.g., Mg-Zn [3], Fe/ZnS bone-repair material [11]), energy (e.g., neutron tube shells [8]) and micromachines (e.g., programmable micro-robots [5]).…”

“…Tao et al [5] demonstrated a novel femtosecond LAM process with smart materials for soft interactive hydrogel micro-machines. These programmable stimuli-responsive matrices mechanized hydrogels into robotic applications at the micro/nanoscale (<300 × 300 × 100 µm 3 ).…”